1. Field of the Invention
This invention relates to a printing apparatus which enables coating operation as needed in addition to numbering and imprinting.
2. Description of the Prior Art
Printed matters which require a good-looking appearance such as book covers, catalogs, and pamphlets are often coated with a varnish which forms a film on the printed paper to prevent the surface from staining and give it a gloss. The coating operation may be performed by an independent device (coater), but in many cases it is carried out by a coater provided in a delivery passage of a printing apparatus to perform the coating operation immediately following the print operation for improved working efficiency.
On the other hand, in some cases, a numbering and imprinting device is provided in the delivery passage of the printing apparatus for partial imprinting or numbering. In the numbering and imprinting device, a numbering device can be attached to a printing shaft to perform numbering, or a relief imprinting cylinder in place of the numbering device can be attached to the printing shaft to perform imprinting.
In prior art printing presses, the coater or the numbering and imprinting device is provided as an independent device.
As described above, since the coater and the numbering and imprinting device are separate devices in the prior art printing presses, both devices must be installed when a coating operation is required in addition to numbering and imprinting operations, which result in an increase in equipment cost and installation space.
When one designs a printing apparatus that can perform the coating operation in addition to the numbering and imprinting operation, there occur the following problems. The printing shaft of the numbering and imprinting device is normally divided into shaft supporting sections at both ends of the shaft and a central section to support the numbering device or the like, in order to facilitate attaching and detaching of the numbering device or an relief imprinting cylinder to and from the printing shaft and cleaning of an impression cylinder which is located at the rear side of the printing shaft. Thus, only the central section of the printing shaft can be removed from the printing apparatus, and the numbering device or the relief imprinting cylinder can be attached to the removed central section of the printing shaft, thereby facilitating attaching the device. Further, the removal of the central section of the printing shaft results in a space in the printing apparatus, which facilitates cleaning the inside of the printing apparatus. However, since the central section of the shaft is detachably mounted on the shaft supporting sections with retaining means such as bolts, the central section can possibly be mounted eccentrically relative to the shaft supporting sections with restricted mounting accuracy. For the case of the coater, a coating cylinder to coat a varnish or the like on the print paper in combination with the impression cylinder is required to make exact rotation. If the coating cylinder rotates eccentrically, the distance between the coating cylinder surface and the impression cylinder varies as it turns with a variation in contact pressure, which results in uneven thickness of the coating layer. Since a quick-drying type varnish is used, all of the varnish supplied to the coating cylinder must be transferred to the paper surface. However, if there is an eccentric rotation of the coating cylinder, flow of the varnish is interrupted and the varnish hardens on the coating cylinder, which results in increased unevenness greater than due to the eccentric rotation of the coating cylinder. Therefore, printed matter with enhanced gloss cannot be obtained. As compared with numbering, coating requires an increased printing pressure. However, if the central section of the printing shaft is fastened with a bolt, the central section is liable to shift in the direction perpendicular to the axis of the bolt, which results in an increased eccentricity and vibration. Therefore, it is practically impossible to attach the coating cylinder to the central section of the printing shaft.
Further, since normally the prior art coating cylinder has been integrally combined with the shaft supporting sections, the whole frames supporting the coating cylinder must be dismantled to remove the coating cylinder, which has made it difficult to remove and replace the coating cylinder.